Do All Female Mammals Menstruate Like Humans?

Anyone who has experienced a period knows the frustration, inconvenience, and oftentimes, pain of enduring this natural part of the reproductive cycle. But just how natural and useful are periods really — especially as we look at the rest of the animal kingdom?

To imagine animals dealing with the same kind of cycle in the wild seems almost ridiculous, but humans can’t be the only ones who experience it.

As it turns out, we aren’t. However, we aren’t far from being alone in this.

Menstruation has been found in different mammal groups, but it’s generally limited to primates. This includes our closest relatives, such as chimpanzees, monkeys and apes. Beyond those creatures, though, menstruation only occurs in four bat species, as well as elephant shrews.

If that seems like a random selection to you, then you’re not alone. The exact reason as to why this specific group of animals undergoes this cycle remains unknown. And if you’re wondering about animals like dogs and cats, they experience an entirely different process.

Now to get into some of the details. Menstruation, as you’ve hopefully learned, describes the shedding of the uterine lining. To be slightly more specific, “The inner lining of the womb, known as the endometrium, prepares for an embryo to implant in it. The endometrium thickens, divides into different layers and develops an extensive network of blood vessels.”

Overt menstruation, that process which we know and loathe, is “where there is bleeding from the uterus through the vagina, [which] is mostly found in humans and close relatives such as chimpanzees.”

Beyond primates, some bats and the elephant shrew, other placental mammals undergo a process where the endometrium is reabsorbed into the body, a process sometimes called concealed ovulation.

As lovely as that would be for humans, apparently, our lining is too thick to be reabsorbed. Researchers have been trying to discover the evolutionary reason behind this biological phenomenon, and while some interesting theories have been presented, we still don’t have a definitive answer.

Why, then, do some animals have thicker uterine linings that can’t be easily reabsorbed without any of the messy nuisance of bleeding? More importantly, why don’t humans function in the same way?

This difference, from what researchers have learned at this point, seems to center on how much control a mother has over her womb.

It’s not conscious, of course, but based on hormones. In these species, the mother’s hormones determine the thickness of the uterine lining, which helps the embryo implant in the womb wall. In most other mammals, it’s the embryo that signals the womb to produce a thicker lining. At least, this is the current theory, according to a 2011 paper published by Deena Emera of Yale University.

The reason for this difference remains unknown, but there some interesting theories exist.

Maybe it’s because humans, and several other animals, mate outside of a normal ovulation cycle. That leaves a greater chance for less-than-optimal timing for egg fertilization, which can lead to genetic problems with the embryo.

It might also be due to more aggressive fetuses that dig deeper into the uterine lining in order to access the mother’s blood supply, unlike, say, pigs and horses, whose embryos sit lightly on top of the womb lining.

Or maybe there is no specific reason, and this is just how our disparate species have adapted.

Regardless, feel free to send some sympathetic acknowledgements out not only to our fellow primates, but also bats and elephant shrews. We’re all in this together.

Photo Credit: Robert Moran/Flickr


Maureen G
Maureen Gyesterday

Interesting article.

Georgina Elizab M

Interesting tyfs

Panchali Yapa
Panchali Yapa2 days ago

Thank you

Carl R
Carl R2 days ago

Thank you Care2!!!!!

heather g
heather g3 days ago

Thanks for that info....

Nicole H

@ Tara b : thank you very much for this additional info. I did not know about horses. And indeed dogs are only fertile during their bleeding period. That's why I kept my dog very short on the leach during her bleeding, as male dogs were way too curious !!

@ Therese Kutscheid : I don't think we humans have menstruations, because we know how to handle them.... What about all the primates then, chimps, bonobo's and others also have their "periods". Do they know how to handle it ??

@ Freya H and Karen H : I fully agree with both of you. Indeed, even in 2017, there are a lot of young girls who have not the slightest idea of what their menstruation really means, what causes it, aso... Disgraceful that sexual education in schools is so very poor, or even non existent and that parents don't take the time to inform their daughters. Those girls have intercourse when they are 13/14 years, but don't even know during what which days she is the most vulnerable to get pregnant. And this would be the beginning of good birth control and avoiding so much abortions.

Something else : I even heard once from a female zoo keeper, who was working with the bonobo's (like chimps but a little smaller) after a certain period of time adapted their "periods" to the menstruation time of their care takers. So they had their bleedings at the same time. If this is true ?? I don't know, but I would not know why this woman sho

Nicole H

Very interesting article. However, having had several dogs, we always had females, apart from 1 Belgian Shepherd dog (Malinois). All our female dogs also had bleeding at more or less regular intervals. The big dogs we had were all sterilized, so I can not tell about them, but the last one was a mix terrier, and due to various circumstances, she was not. Twice a year, she had bleedings. Not exactly every 6 months, but averagely between 5 and 8 months. They even sell special small panties and protection pads in various sizes in the pet shops Her bleedings lasted for about 2 to 2 1/2 weeks, and when she had her heavy bleedings during about 1 week, I always put on such a special panty. Which of course I had to remove these when going outside, and keeping my dog very closed to me , because the males were highly interested in her, big and small ones.... As far as other mammals are concerned, I really do not know. But anyway, I have never seen something like that with the rabbits we had.

Filomena C
Filomena C3 days ago


Philippa P
Philippa P4 days ago


Ruth C
Ruth C4 days ago

Its bad enough that we human females have it, I'm glad that so many animal mammals don't!